SA man died from toxic drug cocktail

An Adelaide man died from a toxic cocktail of drugs including morphine, valium and tramadol which had all been prescribed to his partner, a court has been told.

NSW woman Wendie-Sue Dent is on trial in the South Australian Supreme Court charged with the murder of her de facto husband David Lawrence in December 2015.

Prosector Emily Telfer SC told the jury on Monday Mr Lawrence's death was not the result of suicide or an accidental overdose.

"This was a deliberate killing by the accused of David Lawrence because she stood to gain financially from his death," Ms Telfer said.

The prosecutor said a post mortem examination had found traces of all three drugs in the dead man's blood and traces of those drugs were also present in a glass of orange liquid found next to his bed.

An expert would tell the court the level of morphine found in the 63-year-old's system was the equivalent of him taking 20, 100-milligram tablets.

Ms Telfer told the jury that after the death of Mr Lawrence, Dent, who was brought from Dapto in NSW to face trial, had tried to portray their relationship in such a way as to maximise her chances of benefiting financially.